The requested service 'PAC.ADInterface.Services.IADUserService' has not been registered. To avoid this exception, either register a component to provide the service, check for service registration using IsRegistered(), or use the ResolveOptional() method
to resolve an optional dependency.

Do I need to include something in my module to resolve the dependency? Please help!

You shouldn't have to do anything else. Perhaps your module is not enabled? Did you define this service class in your theme or in your module? If it's in your theme, then something is probably not setup right. I had some issues once where I created some
class in a theme, but was never invoked until I moved that class to a module. However, it (code files) should work in themes as well.